In operation, electrical coupling is produced between the stylus and the digitizer tablet and position of the stylus on the digitizer surface is determined from the coupled signals. A combination of stylus and digitizer tablet is commonly referred to as a "digitizer". The earliest digitizers were mechanical devices with restrained arms. More advanced digitizers have free moving styluses and use various forms of coupling phenomenon between a stylus and a digitizing tablet to determine stylus position. Coupling has been based upon electromagnetic, electrostatic, sonic, piezoelectric, magnetostrictive, optical, etc. principles. The tablet surfaces have included crossed grids of wires, matrices of electrodes and resistive surfaces. Generally, these devices depend upon monitoring of signals introduced into a plurality of X and Y oriented conductors or into a resistive film.
Styluses are generally hand-held devices which press against the digitizer tablet surface with a point similar to that on a conventional ball-point pen. Within the stylus housing are mounted various circuit elements including electrodes for coupling to the digitizer tablet surface where capacitive coupling is used, electrical windings where an inductive coupling is used, etc., as is appropriate for the concept, as indicated above, upon which operation of the digitizer is based. Data from the stylus/tablet combination is input to electronic circuits which convert the signals into data representative of the coordinate position of the stylus on the tablet or into signals which in conjunction with a microprocessor are used to drive a display. The display can indicate either or both the numeric coordinates of the location of the stylus or a graphical representation indicating the stylus position by a displayed dot.
It is desirable for orderly operation of the apparatus and for elimination of spurious data inputs, that the entire system be operative only when the stylus is intentionally pressed against the digitizer tablet surface. For this reason, switching elements are generally included within the stylus housing to isolate the stylus from the data processing circuits or connect the stylus as required in operation. The switching elements are varied in construction and include simple electro-mechanical switches which are actuated by a small movement of the stylus point into the stylus housing when the point is pressed against the digitizer tablet surface.
In another construction, a core is moved within an induction coil when the stylus point is pressed against the digitizer tablet surface and the point recedes slightly within the stylus housing. This core movement changes the output from the induction coil and provides a signal to activate the stylus. Capacitive switching is also used wherein a capacitive plate is connected to the stylus and moves in relation to an opposing capacitor plate when the stylus is pressed against a digitizer tablet surface. This movement induces a signal which activates the system.
Switches operated directly by the stylus user are available in the form of switch buttons and switch handles located on the outside of the stylus housing.
However, a disadvantage in the prior art styluses is the added bulk, complexity, and cost of switches for initiating active use of the stylus as described above. What is needed is a stylus construction including reliable on/off switching or pressure function using small and economical components.
A further disadvantage of the prior art styluses is that substantial tip travel in the axial direction is required to activate the switch.